A "progressive" jackpot is a prize that grows with each stake placed on the games linked to it, and the "counter" (the running display of the prize) is a total of money that other players have already staked. Apart from a starting amount, which the second section explains, the money on the counter comes from the players; the base game returns less, by the share that the counter takes.
This page follows that share from the stake to the prize, with a hypothetical player and the arithmetic of the contribution. It then reads the records paid on Mega Moolah, a network whose wins the provider, the operators and the trade press have announced with dates and amounts (the figures in euros are those of the sources), which is why we can cite them.
Where the money on the counter comes from
Every progressive game sets aside a fixed share of each stake, the "contribution", and adds it to the pot, while the rest of the "RTP" (return to player, explained in our guide to online slots) is paid by the "base game" and its features. The arithmetic is short. Take a hypothetical slot with a total RTP of 93 per cent, of which 4 points go to the jackpot: the base game then returns 89 per cent, and the jackpot pays the other 4 points to whoever wins it.
Our player bets $0.50 a spin for 2,000 spins, so $1,000 in all. Of that, $40 goes to the counter ($1,000 times 4 per cent) and the base game returns on average $890, which means that a player who never wins the jackpot (almost every player, almost every time) loses $110 in expectation rather than the $70 that the headline RTP suggests!
The difference is the price of the "lottery ticket" built into the game; in our view the phrase is a fair description rather than an insult. If you want long sessions at a moderate cost, a progressive slot is the wrong tool, because part of its return is reserved for a prize that almost nobody collects.
The seed, and the share that refills it
After a win the counter does not fall to zero but to a "seed" (the starting value that the network guarantees), and the rules of the jackpot say how that seed is funded, often from a second slice of the same contribution. The slice of each bet that the game announces pays, then, for the current prize and for the next one at the same time.
The seed also explains the arithmetic of a counter that is running high. On a classic progressive, where each dollar staked has the same small chance of the "top prize", the jackpot's share of the return grows with the counter: on our slot, a counter at twice its average winning value (say $10 million against an average of $5 million) lifts that share from 4 to 8 points, and the game returns 97 per cent while the counter stays there.
The extra return goes to the one winner, however. The 89 per cent of the base game is still what everyone else plays against, which is why a high counter raises the expected value of a spin without changing what almost every player takes home.
A licensed casino with jackpot slots
One operator, its licence and its platform, for a player who wants to read a jackpot's rules before betting on the counter.
All Slots
Alderney and KahnawakeAlderney category 1 licence (Baytree (Alderney) Limited) and Kahnawake permit (Baytree Interactive Limited)
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Network, standalone and "must drop" pots
A "network" jackpot links many games at many casinos to one counter, which is how the largest prizes are built, while a "standalone" (or "local") jackpot grows on a single game or at a single casino, and so climbs more slowly and keeps its prizes smaller. The network whose records we read below is of the first kind, and its counter is fed by players in many countries at once.
A "must drop" jackpot adds a ceiling (an amount, or a time such as midnight) by which the prize must be paid, and this is the kind of pot in which the chance of winning really changes with the counter; the closer the counter gets to the ceiling, the closer the drop must be. The rules of the game print the ceiling, and you can read it before the first spin.
The odds of the top prize, as an order of magnitude
The odds of the top prize are not always printed. The contribution, however, gives an order of magnitude. Suppose that a network's top prize is won at $5 million on average and that it receives one cent of every dollar staked: it then takes, on average, $500 million of bets across the whole network to fund one winner, so a $1 spin has a chance in the order of one in 500 million.
The figure moves with the assumptions, though not by much, since halving the average prize or doubling the contribution brings the chance to one in 250 million, which is still a number that no session of play comes near. On games where the chance grows with the stake (the rules say so when it does), a smaller stake simply buys you a proportionally smaller ticket.
The records paid on Mega Moolah
"Mega Moolah" (a Microgaming game in the years of the records below, now supplied by Games Global) is a network that has broken its own record more than once. On 6 October 2015 its counter paid €17,879,645 to a British player at Betway, a payout that Guinness World Records lists under the "largest jackpot payout in an online slot machine game".
The counter then paid €18,915,872.81 on 28 September 2018 at Grand Mondial, one of the Casino Rewards brands (as the trade press reported in the first days of October 2018). In April 2021 it paid €19,430,723.60 to a player in Belgium who had staked €15 on "Absolootly Mad Mega Moolah" at Napoleon Sports & Casino (according to the operator's press release of 30 April 2021).
The largest figure belongs to another Games Global jackpot, "WowPot": €38,461,200.95 on 20 December 2023 on the game "Wheel of Wishes", which Games Global's announcement of 4 January 2024 called the "largest online slot jackpot win" (ahead of the €19.4 million of Mega Moolah). At our hypothetical contribution of one per cent, a prize of €19.4 million stands for almost two billion euros of bets from players who did not win it!
What we would read in a jackpot's rules
Before a jackpot slot we would read four lines of its rules: the share of the RTP that goes to the jackpot (when the rules give it), whether every stake is "eligible" or only some, the ceiling if the pot must drop, and whether spins paid with bonus money can win the top prize at all. The last point can be settled by the casino's bonus terms instead of the game's rules, so both texts are worth opening before you play.
The jackpot remains what the arithmetic makes it, a lottery ticket sold inside a slot; we would treat it as such, as a small part of a budget spent on a very small chance, with the base game's return as the true price of the hours played. Why that price shows only over many spins is the subject of RTP and volatility, and the house edge guide sets it beside the tables.
Three more casinos we list
Three operators, each with what we could read of its licence, for a reader who wants to compare before choosing.
Decode Casino
No licence statedNeither the footer nor the terms of the site name a gaming licence or an operating company (read on 16 October 2026)
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Emirbet
Licence not confirmedAn Anjouan licence of Next Global Era Limited is reported by a third-party listing, not confirmed at source
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Fair Go Casino
Licence not confirmedThe site could not be read on 16 October 2026, so its licence and operator are not confirmed
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Questions
How do progressive jackpots work?
A fixed share of every stake on the linked games is added to the prize, so the counter grows until someone wins it and then restarts from a seed value. The base game returns less to pay for it.
Does a higher jackpot mean better odds?
On a classic progressive the chance per spin stays the same and only the prize grows, so a high counter raises the value of a spin for the eventual winner without changing the odds. On a must drop jackpot the drop gets closer as the counter nears its ceiling.
Which is the largest Mega Moolah jackpot paid so far?
The largest reported Mega Moolah payout is €19,430,723.60, paid in April 2021 to a player in Belgium at Napoleon Sports & Casino. A larger prize, €38,461,200.95, was paid by Games Global's WowPot jackpot on 20 December 2023.
What is a must drop jackpot?
A jackpot with a ceiling, an amount or a time, by which it has to be paid. The rules of the game state the ceiling.
Can a progressive jackpot be won with free spins?
It depends on the game and on the casino's bonus terms, which can exclude bonus money and free spins from the top prize. Both texts should be read before playing.
